Self Assessment Tax Return Guide
Self Assessment is the system HMRC uses to collect Income Tax from people whose income is not fully taxed automatically through PAYE. This can include sole traders, landlords, company directors, partners, investors, high earners and people with untaxed income.
Introduction
For many people, the difficult part is not just submitting the return. The real challenge is knowing what income to include, which expenses are allowable, what records to keep and when payment is due.
This guide explains who may need to file, key deadlines published on GOV.UK, what to prepare, common mistakes and how professional support can help.
Who needs to file a Self Assessment tax return?
You may need to file a Self Assessment tax return if you are self-employed, receive rental income, are a partner in a business partnership, have Capital Gains Tax to report, receive foreign income, receive dividends or savings income above relevant limits, or have been asked by HMRC to submit a return.
HMRC provides an online checker on GOV.UK to help confirm whether you must send a Self Assessment return for a given tax year.
Key Self Assessment deadlines
For online Self Assessment, HMRC sets the filing deadline each year on GOV.UK. For the 2024/25 tax year, HMRC stated the online deadline was 11:59pm on 31 January 2026. If you wanted HMRC to collect eligible tax through your tax code, the return usually had to be filed by 30 December 2025.
For the 2025/26 tax year, the online return deadline is typically 31 January 2027 under the usual cycle. HMRC’s Making Tax Digital timeline also references 31 January 2027 for submitting the 2025/26 return in the standard way. Always confirm the latest dates on GOV.UK.
What should you prepare?
Before starting your tax return, gather:
- UTR and National Insurance number
- employment income details
- P60, P45 or P11D
- self-employed income records
- business expenses
- rental income and property costs
- bank interest
- dividend vouchers
- pension contributions
- Gift Aid donations
- CIS statements
- capital gains records
- foreign income details
- previous payments on account
Good records help reduce errors and make it easier to claim valid expenses.
Common Self Assessment mistakes
Common mistakes include missing income, claiming personal expenses, forgetting rental income, missing CIS deductions, ignoring payments on account, using poor records, filing late and paying late.
A solid return is about reporting income correctly, claiming valid reliefs and keeping evidence in case HMRC asks questions later.
How DepoTax can help
DepoTax helps individuals, sole traders, landlords, contractors and company directors with Self Assessment tax returns across London and the UK.
We can help prepare your return, review your records, calculate tax due, explain payments on account and submit the return to HMRC.
Frequently asked questionsFAQ
Who needs to file a Self Assessment tax return?
You may need to if you are self-employed, receive rental income, are a partner, have CGT or foreign income to report, receive dividends or savings income above relevant limits, or HMRC has asked you to file.
When is the online Self Assessment deadline?
HMRC publishes deadlines each year on GOV.UK. For example, for the 2024/25 tax year the online filing deadline was 11:59pm on 31 January 2026; the following cycle typically follows the same January pattern.
What records should I gather?
Typically your UTR, NI number, employment forms (P60, P45, P11D where relevant), business income and expenses, rental records, bank interest, dividends, pensions, Gift Aid, CIS statements, gains and foreign income.
Can DepoTax help with Self Assessment?
Yes — DepoTax prepares and reviews Self Assessment returns for individuals, sole traders, landlords, contractors and directors across the UK.
Related DepoTax services
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